目 underneath is the eye radical and locks the meaning down: 瞥 is something the eye does, specifically a quick darted glance. It groups 瞥 with 看 (look), 瞧 (peep), and 瞄 (aim a glance), the family of seeing verbs.
敝 sits on top and supplies the reading, shifting from bì to piē in the same labial cluster. The same phonetic appears in 蔽 (cover) and 弊 (defect), and adds a flavor of something fleeting and imperfect — fitting for the brief glance 瞥 names.
